Add a trace event for IntersectionObserver computing intersections.

third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/IntersectionObserverController.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/IdleRequestOptions.h"
+#include "platform/TraceEvent.h"
 
 namespace blink {
 
 IntersectionObserverController* IntersectionObserverController::create(Document* document)
 {
     IntersectionObserverController* result = new IntersectionObserverController(document);
     result->suspendIfNeeded();
     return result;
 }
 
@@ skipping 44 matching lines @@
         return;
     }
     HeapHashSet<Member<IntersectionObserver>> observers;
     m_pendingIntersectionObservers.swap(observers);
     for (auto& observer : observers)
         observer->deliver();
 }
 
 void IntersectionObserverController::computeTrackedIntersectionObservations()
 {
+    TRACE_EVENT0("blink", "IntersectionObserverController::computeTrackedIntersectionObservations");
     for (auto& observer : m_trackedIntersectionObservers) {
         observer->computeIntersectionObservations();
         if (observer->hasEntries())
             scheduleIntersectionObserverForDelivery(*observer);
     }
 }
 
 void IntersectionObserverController::addTrackedObserver(IntersectionObserver& observer)
 {
     m_trackedIntersectionObservers.add(&observer);
@@ skipping 11 matching lines @@
 
 DEFINE_TRACE(IntersectionObserverController)
 {
     visitor->trace(m_trackedIntersectionObservers);
     visitor->trace(m_pendingIntersectionObservers);
     ActiveDOMObject::trace(visitor);
     IdleRequestCallback::trace(visitor);
 }
 
 } // namespace blink